The non-structural genes of the rubella virus code for the proteins which are involved in the replication complex such as RNA-dependent RNA polymerase. In order to understand the mechanism of rubella virus replication in the attenuated strain we undertook studies to analyze the structure of the nonstructural genes. A cDNA library of the non-structural genes of the vaccine type virus RNA (HPV-77) was constructed using specific oligonucleotide primers corresponding to the 5'-end of the structural genes. Several CDNA clones were isolated and identified to be corresponding to the non-structural region. These clones were subcloned into the plasmid vectors for nucleotide sequence analysis. In addition, these clones are being used to isolate clones which will represent the entire non-structural region. Nucleotide sequence analysis of some of these clones has revealed the structure of nsP3 and nsP4. Currently nucleotide sequence of the nspl and nsp2 genes is being determined. Using PCR technique, various regions of the non-structural and structural genes are being put together to make infectious cDNA clone which will enable us to study the effect of mutations on the viral replication.